The present invention relates to a polyphase motor (such as a two-phase, three-phase or four-phase motor) driving apparatus and the driving method thereof.
In case of controlling the speed/torque of, for example, a conventional three-phase motor, as seen in the driving of an inverter in an induction motor or synchronous motor, there have been employed a method of chopping six switching elements which are constituent elements of an H-type bridge circuit by high frequency, changing current carrying duty, generating and driving a sine wave current and controlling the frequency of the pseudo-sine wave without detecting the position of a rotor, and a driving method, referred to as a six-step inverter driving method, of applying a rectangular wave voltage to a three-phase coil terminal for every 120.degree.. To control the speed/torque of the motor, the frequency of an applied voltage is changed or a voltage between very low resistors connected in series with the respective phase coils is fed back by a control method referred to as PWM (pulse width modulation) control to interrupt main current, thereby changing an average current value.
In case of, for example, a three-phase motor control system which is not shown, transistors are connected between a terminal +E and a ground and coils of the motor in respective phases are connected to the nodes among the transistors. A speed instruction pulse for controlling rotation speed is inputted from a microcomputer to an AND gate circuit and the rotation position of the motor is detected by a position detection signal generating circuit having hole elements every time a rotor rotates by 30 degrees. A position detection signal generated therefrom is inputted to the AND gate circuit through a delay circuit. The delay circuit is intended to control the position detection signal to delay the signal to thereby adjust timing for supplying the position detection signal to the AND gate circuit. The delay quantity is controlled by the microcomputer, depending on a loaded state or an accelerated state.
The AND gate circuit obtains the logical product between the speed instruction pulse from the microcomputer and the position detection signal from the delay circuit and outputs the logic product output to a six-step ring counter. The ring counter sequentially changes outputs to the six output lines according to the input of the logic product output from the AND gate circuit to the counter repeatedly to thereby supply the outputs to an inverter IC. The inverter IC takes in the outputs from the ring counter, to thereby switching-control the respective transistors so that the transistors operate in accordance with the order of phase excitation steps or the reversed step order.
If the driving circuit stated above is employed, it is possible to synchronize the rotation position of the rotor of the motor with the speed instruction pulse in the AND gate circuit.
Further, in a three-phase brushless motor, transistors connected in series with coils corresponding to three position detection elements are switching-controlled by the outputs of the position detection elements so that the rotation speed matches with the torque of the load. The PWM control is widely used for this speed control as well.
Namely, in the conventional three-phase motor, Y or .DELTA. connected lead lines in A, B and C phases are connected to the nodes of the transistors in the serial circuit, respectively and the directions of voltages between the lead lines are changed to forward or backward directions to drive-control the motor or a one-phase excitation or one to two-phase excitation system for sequentially turning on/off the three elements is used to drive-control the motor.
In those cases, however, since control over the high-side transistors is very complicated, an inverter IC requires transmitter circuits and transformers. Thus, the conventional control system has disadvantages in that circuit space widens and cost increases. Moreover, torque variation is large in the one-phase excitation type driving system. Due to this, the conventional control system has disadvantages in that efficiency is lowered and the motor for generating the same torque is made large in size. Besides, it is required to provide three position detecting sections such as hole ICs within the motor. Thus, motor space disadvantageously increases to thereby make the motor large in size.
Furthermore, in the conventional three-phase motor system, the driving transistors are not necessarily turned on/off instantly at a timing at which a signal is transmitted from the position detection elements. Due to this, the present, precise position of the rotor does not reflect the timing of switching the phase of a driving signal in a real time manner. As a result, it is not possible to supply a driving signal to the stator at optimum timing in consideration of the present rotor position, so that the conventional system cannot obtain the highest efficiency.